Anode For Li-ion Batteries Research Articles

Polymer-based solid electrolyte interphase for stable lithium metal anodes

The uncontrolled formation of a heterogeneous solid electrolyte interphase (SEI) and the growth of dendrites prevent the use of lithium metal anodes in Li-ion batteries. Possible strategies addressing these problems...

Advancements in MoS2‒based Anodes for Li-Ion Batteries: Recent Progress, Challenges, and Future Directions

Significant progress has recently been made in the development of new materials for energy storage and conversion. One of the commercially dominant energy storage technologies is lithium-ion batteries (LIBs), which...

Graphitic carbon nitride (g-C3N4) as an electrolyte additive boosts fast-charging and stable cycling of graphite anodes for Li-ion batteries

This study enhances the cycle and rate performance of graphite anodes in LIBs by adding g-C3N4 to the electrolyte. The g-C3N4 additive optimizes the solvation structure and SEI, enhancing the structural stability and reaction kinetics of graphite.

Large Alkylammonium Cation Based 2D-3D Hybrid Perovskite with Fast Charge Conduction for a Li-Ion Battery Anode

Large Alkylammonium Cation Based 2D-3D Hybrid Perovskite with Fast Charge Conduction for a Li-Ion Battery Anode

Lanthanoid Sesquioxide Ultrafine Nanoparticles on Graphene via General Approach of Ultrafast Redox Reaction and Their Performance as Anodes in Lithium-Ion Batteries.

Herein, we propose a general route of obtaining reduced graphene oxide and metal oxide nanocomposite, demonstrated by cerium, dysprosium, and neodymium sesquioxides, via ultrafast redox reaction (URR). This method utilizes a very fast heating of graphene oxide and a metal salt without any chemical solvents or special reactors. Off the scene tests showed that different ratios of graphene oxide to metal salt change the metal oxide particle size. Morphological, structural, physicochemical, and electrochemical properties were investigated. It was proved via X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data that it was also possible to oxidize dysprosium acetate and neodymium nitrate at 300 °C, which normally would require much higher temperatures. As-obtained nanocomposites were tested as anodes in Li-ion batteries, but their applications should be further expanded to different fields. As Li-ion anodes, they delivered capacity as high as 1173 mAh/g at 0.05 A/g. Interestingly, ex situ measurements of the anode material showed that upon charging ceria is activated to form multiwalled carbon nanotubes. In this respect, we believe that the URR route is an ultrafast method (lasts in an eyeblink emitting colorful sparkles and smoke) to design graphene/metal oxide nanocomposites with tuned nanoparticle size at lower temperatures and without solvents which represents a facile and environmentally friendly approach for various applications.

Electrode-Level Modeling of Silicon Anodes for Improved Cell Design

Abstract Silicon has a remarkably high specific capacity as a Li-ion battery anode material; however, its large volume expansion and contraction make it extremely challenging to use. This work introduces a pseudo-2D (P2D or Newman-type) model that incorporates the distinctive mechanical and electrochemical behaviors of porous electrodes with large volume changes characteristic of silicon and similar active materials. Localized volume change is propagated rigorously to other electrode variables, considering elastic, plastic, and chemical strains; associated advection and hysteresis; the presence of a fluid reservoir and packaging adjacent to the cell stack; nonlinear electrode swelling behavior; deactivation of active material; and the effect of stress on open circuit potential. A silicon half-cell model is carefully parameterized by previously published experiments, and indeed provides insights in how to interpret the experiments and shows where some are problematic. The model is used as a digital twin to predict the degree of electrode utilization for different packaging designs and active material loadings, thereby allowing improved cell design.

Eliminating the crystal water in hydrated iron fluoride towards fast and high Li-ion storage capacity with ultralong cycling stability

Fluorides as conversion electrodes show great promise for Li-ion batteries due to their high theoretical capacity. However, their use is limited by low electronic conductivity and slow reaction kinetics. Additionally, fluorides usually contain crystal water in their structure, and the impact of this water on their performance is not well understood. Herein, we created FeF3@CNF nanofibers using simple electrospinning and fluorination processes as a potential anode for Li-ion batteries. These nanofibers, with FeF3 nanoparticles (∼50 nm) embeded in carbon, provide efficient pathways for lithium ion transport. By comparing the performance of FeF3 with and without crystal water through theoretical calculations and kinetics analysis, we found that removing the crystal water improves reaction kinetics and reduces mechanical strain, resulting in a significantly higher specific capacity, faster kinetics, and excellent cycling stability. In/ex-situ analytical techniques demonstrate that the rapid Li+ storage in the FeF3@CNF anode is due to a reversible conversion mechanism and particle refinement during cycling. The FeF3@CNF anode shows a kinetic advantage that matches well with activated carbon cathode, leading to superior cycling stability. This work highlights the crucial role of removing crystal water in optimizing fluoride-based electrodes and offers new insights for developing high-performance fluoride-based anodes for lithium-ion capacitors.

Theoretical study on electrochemical and thermal behavior of GNP incorporated anode materials for lithium-ion batteries

In this paper, a theoretical investigation of the electrical and thermal performance of lithium-ion batteries employing an unexplored graphene nanoplatelets (GNP) incorporated lithium titanate (LTO-GNP) anode and lithium manganese oxide cathode is demonstrated by using the COMSOL Multiphysics modeling and simulation. The GNP proportions in the LTO active material matrix are varied from 0 to 3 wt%, to assess the improvements in cell potential, state of charge (SOC), variation in internal temperature, discharging capacity, and battery power density across four selected electrodes. The simulation results have indicated the positive effects of increasing the anode’s GNP concentration on the battery performance, alongside temperature-dependent open-circuit voltage (OCV) and SOC outputs of the battery. The analysis of the effects of thermal conductivity on heat accumulation and dissipation within the battery has indicated that the anode with 3 wt% of GNP consistently performed superior to the other electrodes by providing uniform temperature distribution and enhanced electrical performance by promoting better discharge capacity and power density. The LTO anode with 3 wt% GNP has shown 0.2V more cell potential and also has 12.5% improved thermal conductivity when compared to LTO anode without GNP, contributing to better heat distribution inside the battery. The simulation also emphasized the importance of optimal GNP loading in the Li-ion battery anode to attain more uniform temperature distribution with improved battery health and efficiency.

High-entropy spinel-structured (VCrNiCoMn)3O4 anode for Li-ion batteries

In the quest for improved battery performance, high entropy transition metal oxides (HEO-TM) have emerged as potential candidates for lithium-ion battery (LIB) anodes due to their high capacity resulting from multi-electron transfer redox reactions. This study a synthesized spinel high-entropy oxide (VCrNiCoMn)3O4 using a surfactant-assisted hydrothermal method and subjected it to annealing at different temperatures. XRD analysis revealed that the stabilized spinel phase formed at 1223 K. The (VCrNiCoMn)3O4 demonstrated a significant discharge capacity of 1269 mAh g−1, accompanied by a charge capacity of 1030 mAh g−1. After 1000 cycles, it achieved a reversible capacity of 733 mAh g−1. Furthermore, superior rate performance was observed, demonstrating a high reversible capacity of 394 mAh g−1 at a scanning rate of 2 mV s−1. The superior performance was attributed to multivalent species, including vanadium, which stabilizes charge transfer, facilitates redox reactions, enhances electrical properties, and improves structural stability. Vanadium's ability to transition through multiple oxidation states reduce volume expansion, improve structural rigidity, and contribute to cycling stability. Moreover, Kinetic analysis showed that the lithiation reaction was dominated by the Faraday mechanism, while delithiation involved both capacitive and Faraday contributions. These results suggest that incorporating vanadium into high-entropy oxides can optimize electrochemical properties for long-life lithium-ion batteries.

In-situ construction of dual-coated silicon/carbon composite anode for fast-charging Li-ion batteries

Silicon (Si) is regarded as a promising candidate anode for next-generation high-energy–density batteries due to its ultrahigh theoretical capacity of 4200 mAh g−1. However, silicon anodes face tremendous challenges during cycling, including huge volume expansion, highly unstable interfaces and inherently low conductivity. In this study, the dual-coated silicon/carbon composite anode (Si@SiOx@C) with high silicon content of 85 % is obtained by high-energy ball milling and combined with phenolic resin-assisted encapsulation. The amorphous SiOx layer (∼3 nm) facilitates the rapid Li+ transport and mitigates the volume expansion, while the hard carbon layer (∼3 nm) improves the electronic conductivity and helps to protect against silicon oxide layer erosion from electrolyte, synergistically contributing to the fast-charging performance. With the synergistic effect of dual coating, the Si@SiOx@C anode shows a high initial Coulombic efficiency of 91 % and maintains a high capacity of 1250 mAh g−1 even after 500 cycles at a high rate of 4 A/g. Moreover, the volume expansion of silicon anode during cycling is significantly reduced. This work provides a novel strategy for high silicon content anode in developing fast-charging batteries through dual-coating regulation.

Pillared Graphene Nanostructures for Electrochemical Energy Storage

The global electrochemical energy storage market ranging from electric vehicles and personal electronics to physical grid storage and defense applications demands the development of new classes of materials for fabricating high performance batteries and supercapacitors. I will begin by describing innovative approaches for the design and synthesis of nanostructured carbon materials towards enhanced reversible capacity; superior rate performance and cycling stability; and superior gravimetric capacitance. A novel 3D architecture called a pillared graphene nanostructure (PGN) is a combination of two allotropes of carbon, including graphene and carbon nanotubes possessing ultra large surface area, tunability, mechanical durability and high conductivity can be grown on a variety of substrates, which are appealing to diverse energy storage systems. Another type of 3D superporous carbonaceous architecture called chrysanthemum nanofibers can be grown in roll-to-roll form on commercial nickel foams. Integration of nanostructured pseudocapacitive metal oxides to such 3D templates can provide superior electrochemical performance in supercapacitor applications. PGN templates can also be transformed into cone-shaped clusters decorated with amorphous silicon for advanced lithium ion (Li-ion) battery anodes. Single and multilayer stacked 3D carbonaceous architectures could also be envisioned for further future applications in hydrogen storage. I will also describe recent advancements in upcycling polyethylene terephthalate (PET) waste into active nano-carbon electrode materials for energy storage. For PET plastic-waste, materials are dissolved in a mixture of trifluoroacetic acid and dichloromethane, followed by carbonization under an argon/hydrogen atmosphere. Electrodes derived from PET are employed in supercapacitors and Li-ion battery anodes. Our studies pave the way for scaled up manufacturing of energy storage devices with enhanced energy density and power density.

Lithium, Ether, and Graphite: A Retrospective Trilogy of the Anode-Electrolyte Interface

Ethers represent a family of solvents widely applied in various battery chemistries, except in the most successful battery—Li-ion batteries (LIBs). It is believed that ether electrolytes are incompatible with graphite anodes in LIBs due to detrimental solvent co-intercalation and exfoliation. Here, we demonstrate that ether electrolytes at standard salt concentration can enable outstanding reversibility and fast-charge capability of graphite anodes in LIBs. In short, for ether electrolytes, the anion and the solid-electrolyte interphase (SEI) govern the electrochemical behaviors of graphite anodes. Firstly, we point out that exfoliation and co-intercalation are not always the root causes of the documented cell failures using graphite anodes. Matching the reductive stability between solvents and salts is key to resolving the interphase problem. Reductively unstable lithium bis(fluorosulfonyl)imide (LiFSI) is the optimal salt paired with 1,3-dioxolane (DOL), enabling weakened Li-solvent interaction, preferential reduction of the FSI anion, and a homogeneous SEI enriched with inorganic species. Consequently, electrolyte reduction and Li-DOL co-intercalation are inhibited. Secondly, reductively stable LiBF4 paired with dimethoxyethane (DME) realizes improved cyclability of graphite based on a cointercalation mechanism. We conducted a holistic investigation into the nature, function, and formation of the heterogeneous SEI. Specifically, we revealed a self-terminating, heterogeneous interphase based on grainy LiF located on the catalytically active edge plane of natural graphite. Thirdly, we discovered a novel cointercalation mechanism, namely, in-situ synthesis of ternary graphite-intercalation compounds in a new electrolyte. We characterize the progressive cointercalation via operando synchrotron X-ray analyses, supporting reduced volume expansion and high structural integrity of the cointercalated graphite. The resulting t-GIC chemistry delivers unprecedented fast charging (1 minute) and ultralong lifetimes exceeding 10,000 cycles. The full cells based on cointercalated graphite display remarkable cycling stability upon a 15-minute charging and excellent rate capability even at -40°C. In these three case studies combined as a trilogy with strong correlation, we clarify a long-standing confusing issue in the LIBs community—that is, the compatibility between ether electrolytes and graphite anodes. This trilogy summarizes and reflects on past experiences with the anode/electrolyte interface (mostly failures of ether electrolytes when cycling graphite anodes) dating back to the 1970s. Learning from history, we exemplify different intercalation chemistries of graphite based on DOL, DME, and another common ether solvent, paired with 1M lithium salts, all showing approximately 99.9% Coulombic efficiency, high capacity retention, and rapid interphase kinetics. Our findings not only shed light on the enigmatic interphase formed by ether electrolytes but also offer critical insights into future electrolyte design for graphite anodes operated under extreme conditions.

Listening to Batteries: Utilising Acoustic Characterisation Techniques to Optimise Formation Cycle Protocols in Lithium-Ion Batteries

The optimisation of the formation cycle in battery manufacturing plays a crucial role in driving the success of the electric revolution. The formation cycle, which involves the initial charging and discharging of lithium-ion batteries (LIB)s to stabilise their electrochemical processes, directly impacts the overall performance and longevity.1 This formation process of LIBs is the most expensive and time-consuming step in the total battery pack cost and process, meaning it is a critical bottleneck in the manufacturing industry and requires substantial capital equipment to deliver reliably.2,3 The long duration is required to ensure that a stable layer of surface interphase grows between the electrode and electrolyte, known as the Solid Electrolyte Interphase (SEI). A stable SEI layer is essential to minimise active lithium loss, electrolyte depletion and capacity fade over the lifetime of the battery, as well as mitigating safety issues within the cell and pack.4 It is therefore vital to develop novel characterisation techniques to improve this formation process.Acoustic methods are one of the most promising diagnostic and characterisation techniques for batteries. The technique offers the potential for a real-time operando prediction of the State of Health (SoH), State of Charge (SoC) and State of Safety (SoS).5–7 Broadly, acoustic techniques can be divided into Acoustic Emission (AE) and Ultrasonic Testing (UT) methods; each slightly differs in terms of purpose and experimental setup. Both techniques can detect the physical and electrochemical changes within the cell during usage such as gas formation and cracking.8 In this work, conducted at UCL under the Faraday Institution's SafeBatt project, we use a combination of Acoustic Emission and pulse-echo Ultrasonic Testing in a novel dual-sensor approach. Utilising the sensors, we detect the growth of the solid electrolyte interphase (SEI) during the cell's formation cycle under different protocols and with varying additives. Additionally, we investigate the influence of this SEI layer on the long-term performance and State of Health (SoH) of the cell.We then developed bespoke formation protocols with voltage holds, using acoustic techniques to determine the point at which SEI formation finished and the corresponding success of the passivation layer. This technique can characterise how successfully a cell has formed based on the acoustic signals released, offering a low-cost, non-invasive, and non-destructive approach. We correlated the acoustic results to X-ray photoelectron spectroscopy (XPS), X-ray Computed Tomography, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and in-situ gas volume measurements to confirm the hypotheses made from the acoustic measurements. The results confirmed that as the C-rate increases, a greater amount of acoustic activity is observed, which is attributed to gas formation. Based on the acoustic emission (AE) activity, we were also able to determine the exact voltage at which chemical reactions occur in the electrode electrolyte interphase, including the point where the SEI was developing during the formation cycle. These findings demonstrate the potential for employing acoustic sensors in industry as an advanced characterisation technique to enhance the formation cycle process. References Alptekin, H., Pathan, T.S., Rashid, M., Walker, M., and Widanage, W.D. (2021). Active formation of Li-ion batteries and its effect on cycle life.Leißing, M., Horsthemke, F., Wiemers-Meyer, S., Winter, M., Niehoff, P., and Nowak, S. (2021). The Impact of the C-Rate on Gassing During Formation of NMC622 II Graphite Lithium-Ion Battery Cells. Batter. Supercaps 4, 1344–1350. 10.1002/batt.202100056.Iii, D.L.W. (2019). Formation Challenges of Lithium-Ion Battery Manufacturing. Joule 3, 2884–2888. 10.1016/j.joule.2019.11.002.Wu, J., Ihsan-Ul-Haq, M., Chen, Y., and Kim, J.K. (2021). Understanding solid electrolyte interphases: Advanced characterization techniques and theoretical simulations. Nano Energy 89, 106489. 10.1016/j.nanoen.2021.106489.Bommier, C., Chang, W., Li, J., Biswas, S., Davies, G., Nanda, J., and Steingart, D. (2020). Operando Acoustic Monitoring of SEI Formation and Long-Term Cycling in NMC/SiGr Composite Pouch Cells. J. Electrochem. Soc. 167, 020517. 10.1149/1945-7111/ab68d6.Robinson, J.B., Owen, R.E., Kok, M.D.R., Maier, M., Majasan, J., Braglia, M., Stocker, R., Amietszajew, T., Roberts, A.J., Bhagat, R., et al. (2020). Identifying Defects in Li-Ion Cells Using Ultrasound Acoustic Measurements. J. Electrochem. Soc. 167, 120530. 10.1149/1945-7111/abb174.Fordham, A., Milojevic, Z., Giles, E., Du, W., Owen, R.E., Michalik, S., Chater, P.A., Das, P.K., Attidekou, P.S., Lambert, S.M., et al. (2023). Correlative non-destructive techniques to investigate aging and orientation effects in automotive Li-ion pouch cells. Joule 7, 2622–2652. 10.1016/j.joule.2023.10.011.Fukushima, T., Kato, S., Kuwata, N., and Kawamura, J. (2014). In-Situ Acoustic Emission Study of Sn Anode in Li Ion Battery. ECS Trans. 62, 215–222. 10.1149/06201.0215ecst. Figure 1

Chemical Prelithiation of Silicon Oxide Anodes for Improved Performance in Lithium-Ion Batteries

Si/SiOX-based materials possess significant potential as an anode in Li-ion batteries, due to their high capacity, stable cycling performance and the volume expansion buffering of the SiOX matrix upon lithiation of silicon nanodomains. However, one of the main challenges is their low initial coulombic efficiency (ICE), due to SEI formation and irreversible parasitic reactions which trap Li ions inside the electrode matrix or at the interface. Prelithiation aims to compensate for the large initial irreversible capacity losses, which can be achieved by introducing active lithium directly into the anode material before cycling.Through chemical prelithiation, the electrode coating or active material powder is brought in contact with a reactive Li-containing precursor solution via immersion, which allows a direct reaction at the surface. The precursor system ideally requires a sufficiently low redox potential to achieve (partial) prelithiation of the SiOX matrix, while minimizing full Si lithiation and Li plating at the electrode surface. Lithium-Arene complexes dissolved in (cyclic) ether solvents have been shown to have adequate reducing strength (0.2-0.3V vs. Li/Li+) to allow these redox reactions.In this study, the effects of chemical prelithiation on the battery performance are evaluated inside a half-cell, mainly focusing on the initial cycles. Additionally, the effect of prelithiation on the morphology and composition of the electrode (active) material will be investigated using electron microscopy (SEM) and X-ray diffraction (XRD), including the effect of air exposure on the phase stability. Furthermore, the chemical state of the sample surface is studied, giving deeper insights into its interfacial reactivity and composition. Ultimately, this study aims to create a better understanding of the advantages and disadvantages of this prelithiation method on Si/SiOX-based anodes, paving the way for the development of more efficient lithium-ion batteries.

A New Approach to Synthesis of Porous Si Anode for Li-Ion Batteries Via Organic-Solvent Assisted Etching

Silicon (Si) has been regarded as a promising anode for Li-ion batteries due to its high theoretical capacity (4200 mAh/g) compared to graphite anode (372 mAh/g). However, it undergoes significant volume changes (~ 300%) during lithiation and delithiation, leading to particle pulverization and continuous electrolyte decomposition on Si surface, which hinders its practical application. The porous silicon obtained by wet etching method using hydrogen fluoride (HF) can accommodate the volume changes and improve the overall performance of silicon anodes. However, HF etching is highly corrosive, leading to the generation of excess heat and bubbling, lower yields, and difficult to scale-up. Furthermore, the water in etchant oxidizes the newly exposed Si, generating more SiOx, which also cause over-etching of Si and worsen electrochemical performance.Herein, we report an organic-solvent assistant etching process for Si anode. In this process, selected organic solvent were mixed with the HF etchant. When micron sized Si/SiOx powder was added to the solution, the organic solvent in the mixed solution will preferentially be absorbed on the surface of Si/SiOx powder and form a shield which can enable controlled etching of silicon oxide (SiOx) and prevent direct contact between water and newly etched Si surface. This method leads to controllable etching of Si and avoids bubbling/overheating, results in a higher Si yield. The maximum temperature during the etching process is less than ~30°C. The various process parameters, including etchant composition, stirring speed, and time have been optimized to maximize the yield and electrochemical performance of the Si anode. A Si-based anode with organic-solvent assisted etching process has demonstrated improved cycling performance in a Si||Li(Ni0.6Co0.2Mn0.2)O2 (NMC622) full cell. It also leads to low swelling in both particle and electrode levels required for the next generation of high-energy LIBs. Similar organic-solvent assisted etching process can also be used in safe-etching of a broad range of materials.

Design of Fast-Charging SiO x /Graphite Composite Anodes Via Three-Dimensional Electrochemo-Mechanical Simulations

Enhancing the fast-charging capability of high-energy density batteries is an urgent need for the evolving electric vehicle market. Owing to high theoretical capacities of SiO x , SiO x /graphite composite anodes have garnered great attention for anodes in Li-ion batteries. Higher lithiation potentials of SiO x than that of graphite are beneficial for mitigating Li plating, which is the primary problem under fast-charging conditions. Furthermore, the SiO x /graphite composite anode can reduce cell polarizations due to its reduced thickness compared to that of the graphite anode. However, the significant volume expansion of SiO x upon lithiation poses a challenge to electrode integrity, thereby inhibiting stable cycling. During fast-charging, particularly, the inhomogeneous reaction in the composite anode results in non-uniform volume changes of SiO x particles, causing the development of mechanical stress and the rapid capacity fading.In this study, the reaction kinetics of SiO x /graphite is investigated to design the composite anode with mechanical stability and high electrochemical performance through the three-dimensional (3D) electrochemo-mechanical simulation. We perform simulations on SiO x /graphite composites with various compositions and SiO x distributions to determine the amount of Li plating, anode potentials, and local current densities. In addition to the electrochemical properties, the distributions of mechanical stress and strain within the composite electrode are calculated.The 3D model geometry for the composite anode is stochastically generated based on the result of microstructural analyses. 3D electrochemo-mechanical models are constructed to predict the reaction kinetics in the composite anode. Simulation results show that SiO x particles in the composite anode preferentially react with Li, mitigating the anode potential drop during fast-charging. Also, the composite anode exhibits a more homogeneous distribution of polarization, compared to that of the graphite anode. The mechanical simulation demonstrates that difference in the volume expansion along the thickness increases as the charging proceeds. The predicted significant displacement (strain) at the separator/anode interface is attributed to the preferential reaction of SiO x particles near the separator. This leads to localized mechanical degradation of the composite anode.Furthermore, a bi-layer electrode design with different concentrations, porosity, and particle size of SiO x on top and bottom is suggested through 3D simulation to mitigate mechanical fatigue while maintaining high energy density during fast-charging. The improvement in fast-charging performance is confirmed through electrochemical experiments with the proposed bi-layer composite anode. Both the prevention of Li plating and the reduction of stress distribution are achieved using the bi-layer design. This study offers strategic insights into fast-charging, energy-dense anodes for the development of advanced Li-ion batteries.

Robust Lif–Rich SEI Inducing Protective Layer for High Energy Density Si Anodes in Li–Ion Batteries

As the electric vehicle (EV) market has rapidly grown, the need for Li ion batteries (LIBs) with high energy density is increasing to achieve a longer driving range. However, since the graphite anodes in conventional LIBs have almost reached their theoretical capacity, it is urgently needed to develop a new battery chemistry to meet the demands for long-range EVs. In this regard, Si is considered as the most promising anode materials for high-energy-density LIBs owing to its high theoretical capacity (3579 mAh g-1), low operating potential (~ 0.4 V vs. Li/Li+), and earth abundance. Unfortunately, the employment of Si anodes is hindered by the large volume change (~ 300 %) during the lithiation/delithiation process, which accompanies with electrode pulverization, unstable solid electrolyte interphase (SEI), and continuous electrolyte decomposition.The SEI layer is the interface layer between the electrolyte and anode, which is formed via the reduction of the electrolyte components during the first lithiation process. Typically, the SEI layer is depicted as a mosaic structure that is mainly consisted of organic and inorganic constituents. The organic SEI constituents, which are the byproducts of the decomposition of the electrolytes, show poor Li ion conductivity with an unstable structure. In contrast, the inorganic SEI constituents are ideal SEI components owing to their excellent electrochemical stability. The ideal SEI layer should not only passivate the anode surface and prevent the direct contact of anode surface with the electrolyte, which causes continuous electrolyte decomposition, but also provide exhibit excellent Li ion transfer kinetics. In this respect, LiF is considered as the most ideal SEI component with its stability against the electrolyte and the high Li ion conductivity.To achieve a LiF-rich SEI layer on the Si anode, various strategies have been devised, such as electrolyte additive and LiF coating on the anode surface. The electrolyte additives such as FEC, has been widely used to construct a LiF-rich SEI layer. Unfortunately, the additives are continually consumed over repetitive cycling, which eventually results in a rapid capacity decay of the Si anodes, when they are exhausted. In case of the LiF coating, the coating layer indeed induces LiF-rich SEI layer during the first cycle. However, if the coating layer has insufficient mechanical strength, the severe volume change during the lithiation/delithiation process leads to the breakage of the SEI layer, resulting in uncontrollable electrolyte decomposition and following (re-)formation of the SEI layer. This causes a depletion of electrochemically available Li ions in the electrolyte and a thick-insulating SEI layer with poor Li ion kinetics. Therefore, not only forming an inorganic-rich SEI layer, but also constructing a robust interfacial layer with sufficient physicochemical stability is highly important to achieve stable cycle performances of the Si anodes.In this study, we propose a new strategy to construct a robust LiF-rich SEI layer on the Si anode by employing a LiF-rich SEI inducing protective layer (LPL) comprising of aluminum fluoride (AlF3) and poly(acrylic acid) (PAA) (LPL@Si). In the LPL@Si, the AlF3 induces a LiF-rich SEI layer with high Li ion conductivity, while the polymeric PAA provides a sufficient mechanical strength to alleviate the large volume change of the Si anode. In addition, the PAA in the LPL also acts a role of SEI stabilizer, which promotes the faster formation of the LiF-rich SEI layer owing to the abundant carboxyl groups, resulting in a rapid reduction of Li salts in the electrolyte. Due to these synergistic effects, the LPL@Si anode delivered significantly enhanced electrochemical performances in Li metal cell tests compared to that of the bare Si anode. Moreover, the LPL@Si anode exhibited an enhanced cycle performance than the bare Si anode in a full cell test with a NCM811 cathode. These results prove that our strategy for constructing a mechanically stable LiF-rich SEI layer would initiate further studies for achieving a highly stable Si anode in next-generation high energy density LIBs.

Thin-Shelled Hollow Mesoporous TiO2 Spheres with Less Tortuosity As Fast-Charging Anode

Titanium dioxide (TiO2), abundant in nature and possessing excellent longevity characteristics, is gaining attention as a next-generation anode material for Li-ion batteries. However, compact stacking of TiO6 octahedra induces repulsion between the inserted Li ions, reducing rate performance and achievable capacity. Herein, we propose a hollow mesoporous electrode composed of TiO2 nanoparticles under 30 nm to enhance the interface between the electrode and electrolyte, facilitating the Li-ion movement and promoting a shorter diffusion distance for the inserted Li-ions. Furthermore, the formation of hollow structures enabled Li ions to enter and exit both inside and outside the hollow shell, facilitating rapid charging and discharging characteristics.To produce this hollow mesoporous structure, TiO2 nanoparticles smaller than 20 nm synthesized by a sol-gel process were deposited on a spherical carbon support, and the support was subsequently removed. In particular, the thickness of the hollow shell was controlled to minimize the diffusional path area within the electrode through which Li ions move. Thin TiO2 shells facilitate ion migration via a reduced tortuosity while minimizing isolated pore formation, allowing D Li+ of 3.22×10-11 cm2 s-1 to be attained, 40 times higher than that of bulk-type TiO2. With its rapid Li ion diffusion rate and thin shell, the TiO2 anode exhibited the 70% highest rate capability (10 C vs. 1 C) and a capacity of 221 mAh g-1 at 0.5 C (Fig. 1). The facile Li-ion transport enables the insertion of 0.66 mol Li ions per mole of TiO2 at 0.5 C and 67% rate performance (10 C vs. 0.5 C). When evaluating the rate capability in actual LIBs, a full cell assembled with a LiFePO4 cathode showed a rate performance of 60% (2000 mA g-1 vs. 50 mA g-1), outperforming the 40% for commercial bulk-type TiO2 in a full cell. Hollow mesoporous TiO2 provided a potential anode for fast-charging Li-ion batteries as a thin mesoporous shell allows for rapid ion insertion and extraction with the extended interface of electrode/interface. Figure 1

Robust and Efficient Mechanical Model of High-Volume-Change Silicon Electrodes for Li-Ion Batteries

This work develops an efficient and accurate pseudo-2D (P2D or Newman-type) model capable of describing the relevant mechanical and electrochemical aspects of porous electrodes where the active material undergoes significant volume change. The model is applied to silicon-based anodes for high-capacity Li-ion batteries. While the standard electrochemical equations in a P2D model are well-known, the mechanical equations are less well-established. This presentation will describe the development of mechanical principles and corresponding equations suitable for use in a P2D model.While it is common in previous modeling work for much attention to be spent on the mechanics of the active particles themselves, relatively little attention has been spent on understanding the mechanics of the porous composite electrode. As an example, it is common to treat the expansion of the active material as if it affects only electrode thickness and not electrode porosity. Or it is common to neglect plastic deformation and even elastic deformation of the electrode. And yet both are pervasive in the electrode film under the large chemical strains of lithiation and delithiation.We discuss these and other issues to show complex electrode performance behavior is derived from simple mechanical principles and experimentally derived properties. Shown in the figure below is an example calculation for one set of input parameters, showing how (a,b) porosity, (c,d) film thickness (total strain), and (e,f) tangential (in-plane) stress can change under imposed conditions of external normal stress or lithiation of a pristine electrode. Arrows show direction on a hysteresis loop for a full cycle, caused by plastic deformation of the electrode. Comparison with experiment, where feasible, will also be done. Figure 1

(Invited) A Study of Si-based Metallic Glass Anodes for Li-ion Batteries

Silicon has been considered a promising low-cost negative electrode material for high-energy lithium-ion batteries due to its high gravimetric (400 Wh kg–1) and volumetric energy density (> 800 Wh L–1), low operating voltage (~0.3 V) and abundance in the Earth crust. During the past decades, development of Si-based negative electrodes has been greatly accelerated by modification of morphology, size, composition, and surface engineering. Accordingly, the cycle life of Si-based cells has improved dramatically over the years and is now approaching performance targets showing > 300 Wh kg–1 even after 1,000 cycles. However, as Si is gradually adopted into commercial batteries, the calendar life of the Si-based cells with high silicon content (>40%) is identified to be insufficient (1-2 years) and thus represents a major roadblock to widespread deployment. Interfacial instability of silicon in organic carbonate carbonate electrolytes and continuous electrolyte decomposition lead to a gradual electroyte consumption and shift of active lithium inventory in the cell. A steady growth of the SEI layer accompanies is linked with active lithium loss, which causes severe cell capacity fade and impedance rise. To prevent such a Si negative electrode and cell degradation mechanism, it is essential to exercise better control over the kinetics of electrolyte reduction and SEI layer formation process.Among various approaches to improve the interfacial as well as mechanical stability of silicon, embedding metallic inactive phases into amorphous Si matrix was widely studied. Dahn et al. has demonstrated this idea through a series of studies of over 200 different Si-based amorphous alloys1-3. Amorphous Si-alloys suppress two-phase coexistence of the Li-rich and Li-poor phase which leads to lattice mismatch and crack propagation. Thus, amorphous alloy films showed better capacity retention with less swelling and particle collapse. Furthermore, the inactive metal matrix serves as a buffer for the large volume expansion of Si (~280%), thus improving cycle stability without a significant decrease in the volumetric energy density.In this study we report on the synthesis and evaluation of Silicon-Me amorphous alloys (Me: Ni, Cu, Mn, Ti, Fe) for applications as negative electrodes in high-energy density Li-ion batteries with improved calendar life. Numerous Si-Me metallic glass alloy model electrodes were synthesized, using ultra-fast laser and splat quenching techniques to screen, evaluate, and optimize their electrochemical performance with a focus on the long-term interfacial stability in Li-ion batteries. Si0.85Ni0.15 has emerged as the best performing metallic glass alloy composition and its fabrication was successfully scaled-up with melt spinning technique. The melt-spun Si0.85Ni0.15 thin ribbon was ball-milled into fine powder to be used in conventional composite electrode fabrication for Li-ion batteries. Metallic glass Si0.85Ni0.15 anode showed improved passivation behavior and outperformed a conventional nano-sized Si electrode in both cycle and calendar life tests.AcknowledgementsThis research was supported by the US Department of Energy (DOE)’s Vehicle Technologies Office under the Silicon Consortium Project directed by Brian Cunningham and managed by Anthony Burrell. The work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract no. DE-AC02-05CH11231. This research also used resources of the Advanced Light Source, a U.S. DOE Office of Science User Facility under contract no. DE-AC02-05CH11231; in particular, Beamline 2.4 was used. Melt-spinning production rates and metrics are provided from ECO FM Co. References Fleischauer, M. D.; Dahn, J. R., Combinatorial Investigations of the Si-Al-Mn System for Li-Ion Battery Applications. J. Electrochem. Soc. 2004, 151 (8), A1216.Hatchard, T. D.; Topple, J. M.; Fleischauer, M. D.; Dahn, J. R., Electrochemical Performance of SiAlSn Films Prepared by Combinatorial Sputtering. Electrochemical and Solid-State Letters 2003, 6 (7), A129.Fleischauer, M. D.; Topple, J. M.; Dahn, J. R., Combinatorial Investigations of Si-M (M = Cr + Ni, Fe, Mn) Thin Film Negative Electrode Materials. Electrochemical and Solid-State Letters 2005, 8 (2), A137.